Prevent duplicate equivalency rules and support safe deletion

src/Jiaowu.Api/Controllers/CourseEquivalencyRulesController.cs

@@ -40,6 +40,8 @@ public sealed class CourseEquivalencyRulesController(
             return Forbid();
         if (request.MajorId.HasValue && !await db.Majors.AnyAsync(x => x.Id == request.MajorId && (!collegeId.HasValue || x.CollegeId == collegeId), token))
             return ValidationProblem("适用专业不在当前维护范围内。");
+        if (await HasSameScopeRuleAsync(request, null, token))
+            return ConflictProblem();
         var rule = new CourseEquivalencyRule { OriginalCourseId = request.OriginalCourseId, SubstituteCourseId = request.SubstituteCourseId,
             MajorId = request.MajorId, EffectiveGrade = request.EffectiveGrade, IsEnabled = request.IsEnabled, Notes = request.Notes?.Trim() };
         db.CourseEquivalencyRules.Add(rule);
@@ -58,11 +60,48 @@ public sealed class CourseEquivalencyRulesController(
         var collegeId = scope.Current.RestrictedCollegeId;
         if (request.MajorId.HasValue && !await db.Majors.AnyAsync(x => x.Id == request.MajorId && (!collegeId.HasValue || x.CollegeId == collegeId), token))
             return ValidationProblem("适用专业不在当前维护范围内。");
+        if (await HasSameScopeRuleAsync(request, id, token))
+            return ConflictProblem();
         rule.MajorId = request.MajorId; rule.EffectiveGrade = request.EffectiveGrade; rule.IsEnabled = request.IsEnabled; rule.Notes = request.Notes?.Trim();
         await db.SaveChangesAsync(token);
         return NoContent();
     }
 
+    [HttpDelete("{id:guid}")]
+    public async Task<ActionResult> Delete(Guid id, CancellationToken token)
+    {
+        var rule = await Scoped(scope.Current.RestrictedCollegeId)
+            .FirstOrDefaultAsync(x => x.Id == id, token);
+        if (rule is null) return NotFound();
+        if (await db.CourseSubstitutions.AnyAsync(
+                x => x.CourseEquivalencyRuleId == id, token))
+            return Conflict(new ProblemDetails
+            {
+                Title = "该规则已有课程替代申请引用，不能删除；请改为停用以保留审批和毕业审核留痕。",
+                Status = StatusCodes.Status409Conflict
+            });
+        db.CourseEquivalencyRules.Remove(rule);
+        await db.SaveChangesAsync(token);
+        return NoContent();
+    }
+
+    private Task<bool> HasSameScopeRuleAsync(
+        CourseEquivalencyRuleRequest request,
+        Guid? exceptId,
+        CancellationToken token) => db.CourseEquivalencyRules.AnyAsync(x =>
+            x.OriginalCourseId == request.OriginalCourseId &&
+            x.SubstituteCourseId == request.SubstituteCourseId &&
+            x.MajorId == request.MajorId &&
+            x.EffectiveGrade == request.EffectiveGrade &&
+            (!exceptId.HasValue || x.Id != exceptId.Value), token);
+
+    private static ConflictObjectResult ConflictProblem() =>
+        new(new ProblemDetails
+        {
+            Title = "相同适用范围的等价课程规则已存在。",
+            Status = StatusCodes.Status409Conflict
+        });
+
     private IQueryable<CourseEquivalencyRule> Scoped(Guid? collegeId) => collegeId.HasValue
         ? db.CourseEquivalencyRules.Where(x => x.OriginalCourse!.CollegeId == collegeId.Value)
         : db.CourseEquivalencyRules;